He was about 20 when he won his first gold medal in 72 (Munich). That would have been the time for him to turn pro but he would have had to defect from Cuba to do so. (Back then, Holmes was still one of Ali's sparring partners.)
I think TS would have become either the WBA or WBC champion given some of the other fighters who became champion. Certainly he was as good or better than Mike Weaver, Leon Spinks and John Tate. You also have to figure with benefit of a top drawer trainer he would have developed as a fighter. His game plan was pretty simple, left jab followed by a huge right cross on the button. His punches were very efficient. Classic.
The real debate is how he would have done against Frazier, Foreman, Ali, etc. I think he beats Frazier (who was never the same after the first Ali fight and was a smallish, easy to hit hw with a big left hook.) Foreman, a toss up and they both were upright head hunters. TS had better mechanics but when you hit as hard as Foreman, anything can happen. Ask Micheal Moore. Ali, a stick and move guy, not a knockout puncher but had superior movement and defense. Was well past his prime by 72 but still was good enough to beat/outfox/outbox Foreman (by letting GF punch himself out in the 100 degree+ heat of Zaire at 3 in the morning.) GF fought a truly stupid fight and Ali fought the only fight he could because it would have been suicide to trade blows with GF (even though MA had a great chin.) Assuming he showed up in shape (big assumption), Clay/Ali would have given TS fits because of his unorthodox style. And styles make fights.
Yet another what if scenario
that really can never really be answered.
76 (Montreal) Olympics: TS v John Tate with commentary by some guy who talked funny.
The actual boxing starts around the 3 minute mark.